The purpose of this project is to develop methods for gene transfer to mammalian cells and to use these techniques for gene mapping, analysis of gene expression, and cloning eukaryotic genes. DNA-mediated transformation provides a sensitive bioassay for dominant acting mammalian genes. A recombinant DNA library prepared from cells transformed with DNA from a heterologous species contains only a small fraction of the donor genome. The donor DNA sequences can be detected and isolated after nucleic acid hybridization with a labeled reiterated DNA probe prepared from donor DNA. The clone containing a specific gene then can be identified, using a transformation assay. We are using this method to clone the human tk and hprt genes. Chromosome-mediated gene transfer introduces a relatively large functional chromosome fragment into recipient cells. This procedure has been used for regional gene mapping and transferring closely linked, nonselectable genetic markers into cells. These large transferred genetic fragments also may contain adjacent regulatory sequences and the technique has potential for analysis of gene expression. We have used somatic cell hybridization to map human immunoglobulin genes and sequences homologous with MSV src genes to specific human chromosomes.